Scanning antenna



Filed June l5, 1958 5 Sheets-Sheet 2 END PROPAGATION ENERGY LAUNCHING END Shift Ener Frequency Source of Robert C'. Hansen,

/NvE/vron.

Naw

Arron/Ly,

April 1o, 1962 R. c. HANSEN SCANNING ANTENNA Filed June l5, 1958 5 Sheets-Sheet 3 ATTORNEY.

April 10, 1962 R. c. HANSEN 3,029,432

SCANNING ANTENNA Filed June 13, 1958 5 Sheets-Sheet 4 Rober? C. Hansen,

/NvE/vrof?.

ATTORNEY.

Pfg. 6.

April 10, 1962 R. c. HANSEN 3,029,432

scANNING ANTENNA Filed June 13, 1958 5 Sheeis-Sheet 5 ENERGY LAUNCHING A TTUR/VE Y.

United States Aarent Office 3,029,432 SCANNING ANTENNA Robert C. Hansen, Los Angeles, Calif., assigner t Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware f Filed June 13, 1958, Ser. No. 741,770 11 Claims. (Cl. 343-768) This invention relates to scanning antennas, and particularly to antennas for providing a scanning beam about a selected plane and a given axis in the plane.

The art of generating and controlling electromagnetic wave energy so as to propagate a controlled beam into space includes many movable and electrically controllable arrays. Devices currently in use usually either point a radiating device in the desired direction of propagation or combine the energy radiated from a plurality of individual elements into a single beam which can be varied in direction by appropriate associated means. The devices of the prior art, however, have not heretofore combined the required physical characteristics and electrical characteristics in a satisfactory manner.

For modern applications, such as mobile installations, it is not desirable to have a large movable antenna array for controlling the direction of the emitted beam. It is instead preferable and in many cases even necessary to generate the desired lbeam with a structure which involves only a minimum of inertia. The arrangements of the prior art which have avoided the use of mechanical movement have almost uniformly -been bulky and relatively fragile and have furthermore sulfered in degradation of beam characteristics with the! deviation of the direction of scan from a selected optimum direction.

ln many installations, for example, it is desirable to generate a cosecant-squared elevation beam about an azimuthal plane, and to maintain the cosecant-squared elevation patternV as the beam is moved within a scanning angle about a given axis in the azimuthal plane. Other scanning patterns may of course be desired, but nevertheless it has heretofore been impractical to maintain the desired beam shape, whatever beam is desired, for a large enough scanning angle to be of practical value to a system. The devices heretofore available have therefore been even less suitable for specific applications in which it is desired that the antenna provide an extremely low silhouette or be ush mounted. It may be desired to scan in the forward direction of ymovement of an aircraft, for

example, but without appreciably'increasing the areodynamic drag of the airplane. Such an "antenna installation should not be confined by its nature to a particular location, such as to the limited locations at which it is possible to place a radome or other streamlining structure. Heretofore it has been extremely difficult to provide a directional/scanning antenna which can be mounted substantially flush with a given surface and which can scan without appreciable beam degradation through a considerable angle about a selected direction and in a given plane. The problems of constructing Isuch arrays become greatly complicated when it is further required that the structure be mechanically rigid, that the surface be stable and strong, and that there be no critical tolerances or critical operational characteristics.

Therefore an object of this invention is to provide an improved scanning system for radiating a beam of desired characteristics through a given angle in a selected plane.

Another object of this invention is to provide an antenna for scanning in a given plane, which antenna operates substantially without inertia and` which provides a scanning beam of controlled configuration throughout a considerable angle. -V

It is a further object of this invention to provide an j in the light of the controlled direction.

Yet another object of this invention is to provide a mechanically rigid but physically simple antenna for scanning in a given angle, said antenna providing an external surface which has a minimum extension above a given plane.

It is a further object of this invention to provide an electronic scanning antenna which can be ush mounted in a substantially planar surface but which can scan through a useful angle in the plane of the surface with a beam which Vmaintains its characteristics despite the angle of scan.

Yet another object of this invention is to provide an antenna system for propagating a-lowl side lobe narrow azimuth beam with a cosecant-squared elevation pattern over an acute angle from a surface which is substantially flush with the azmuthal plane.

These and other objects of this invention may be achieved, in accordance with one feature of this invention, by an arrangement using a plurality of phase related radiating elements and an associated wave. trapping surface. The phase related radiating elements may comprise a plurality of slot radiators arranged along an en-` radiators. Energy from the radiators may be directed onto a launching portion of the wave trapping `surface and confined along the length of the wave trapping surface fron; the opposite end thereof. The angle made by the beam with respect to the conductive dicontinuities may become oblique, as the frequency is changed and theV beam is caused to scan, without degradation of the beam shape. Variation'and selection of the gap between discontinuities, the depth of the discontinuities and the configuration of the discontinuities proceeding along the wave trapping surface may be used to insure the desired beam pattern. An energy splash plate member may also be employed to direct energy from the radiating elementsl onto the launching portion of the wave trapping surface.

In accordance with other features of the invention, the nature of the conductive discontinuities, the nature of the wave trapping surface and the arrangement of the energy feed may be altered to derive particular advantageous features. For example, the entire surface may be made completely flush with the 'planar surface in which the array is to be installed, by using a plurality of sinuous feeds having selected phase relations to generate abeam which is inclined onto the wave trapping surface.

In accordance with another feature of tbe invention, an arrangement may be provided which is particularly suited for lower frequency applications, such as in the UHF range. This arrangement may use a plurality of dipole radiators mounted against a ground plane grid and fed by a plurality of ganged variable phase Shifters in the desired phase relation. Wave energy therefrom may be trapped by a plurality of parallel rods spaced apart from a ground plane and arranged in a selected configuration to perform the desired wave trapping function.

The novel features of this` invention, as wellas the invention itself, both as to its lorganization and method of operatiom may best be understood when considered following description, when taken Patented Apr. 1o, lesa frequency from a center frequency.l VAssociated with the line plane may be a wave trapping surface having conductive, discontinuities substantially parallel to the line of the with the result that energy is radiated into spacel in Connection with the accompanying drawing, in which like reference numerals refer to like parts, and in whic FIG. 1 is a perspective View, partially broken away, of an antenna arrangement employing a sinuous feed and a corrugated metallic wave trapping device in accordance with this invention;

FIG. 2 is a perspective view in simplified form of an installation of an electronic scanning antenna, such as shown in FIG. 1, as flush mounted in the wing of an aircraft;

FIG. 3, comprising three diagrams of elevation beam power vs. beam position for three different angles of azimuth scan, and labeled FIGS. 3a, 3b and 3c respectively, shows the effective operation of a device constructed in accordance with the invention;

FIG.l 4 is a simplified view showing a cosecant-squared beam elevation pattern as provided by a device in accordance with this invention;

FIG. 5 is an alternative arrangement of a device in accordance with the invention, showing a different cor-- rugated surface arrangement than is illustrated in FIG. l;

FIG. 6 is a perspective view, partially broken away and in simplified form, of another alternative arrangement of an electronic scanning antenna which may be completely flush mounted in accordance with the invention; and

FIG. 7 is a perspective simplified view, partially broken away, of yet another alternative arrangement in accordance with this invention which is particularly suitable for somewhat lower frequency ranges.

, In accordance withy the invention, referring now to IFIG. 1 there may be provided an electronic scanning antenna which generates a controlled beam in space over a scanning angle lying in an azimuthal plane. An azimuthal planeE as the expression vis here used, is intended to refere4 to any reference plane and not merely to a horizontal plane. The antenna of the present invention may be mounted in a vertical direction or at an angle, and the term azimuthal is used merely to denote the plane of reference which is most easily visualized. Similarly, the fact that the scanning may be said to be donc about a zero direction in the azmuthal plane is again merely employed for they purposes of description. In a given application what may be considered to be the zero direction is purely arbitrary, and may be at any angle with respect to the axis of they present structure.

The scanning antenna arrangement shown in FIG. l therefore may be considered to include a substantially planar wave guiding surface 10 lying principally within an azimuthal plane. The wave guiding surface is of the surface irregularity type employing parallel linear conductive projections or corrugations to confine wave energy. The corrugations in the wave trapping surface 1 0 consists of landsV 12 and grooves 14 in the surface, the direction of the lands 12 being substantially parallel throughout the structure and substantially normal to the zero direction in the azimuthal plane. As shown, the corrugations defined by the lands y12 and grooves 14 may be rectangular. The wave trapping surface 10 may be made of a metallic conductor, with the portion below the grooved surface comprising the ground plane member 16 for the Wave trapping structure 10.

An electronically controllable directional antenna array 20 is mounted substantially parallel and below the azimuthal plane and the wave guiding surface 10 therein. Here again, the term below is used merely to designate a typical relationship for these elements and not to define a limiting relationship. The structure may be mounted upside down, for example, and the operation will not be affected.

The directional scanning antenna 20 may be comprised of a plurality of like rectangular straight waveguides 22 which are substantially parallel to each other. The ends of successive adjacent pairs of these straight waveguides 22 are coupled together by interconnecting arcuate wavein alternating fashion, so that the entire structure 25) forms a continuous sinuous waveguide path for energy to be conducted. In the example shown, the narrow walls 24 of the straight waveguide 22 lie in the same planes and the broad walls 26 lie in parallel planes. One terminal of the continuous sinuous feed antenna 2t) may be taken as an input point or terminal 30 and the terminal at the opposite extremity may be regarded as an output point or terminal 32 and coupled to a load (not shown). Included, in the present example of a scanning antenna 20, are a plurality of slot radiating apertures 40 centrally positioned along a common energy launching line which is transverse to the straight waveguide sections 22. These slot radiators 46 are so positioned, and the lengths of the linear waveguide portions 22 and the interconnecting waveguide portions 28 at the extremities are so selected, that equal path lengths exist between successive apertures 40. Such an arrangement is described more fully in a copending application entitled Frequency Sensitive Rapid Scanning Antenna, Serial No. 374,708, tiled August 17, 1953, by E. Strumwasser and L. C. Van Atta and assigned to the assignee of the present invention. Reference may be made to the copending application `for a detailed description of the operation of this continuous waveguide antenna Ztl. Briefly, however, the application of energy of diiferent frequencies to the input point 30 results in the provision of energy of different phase relation at the slot radiators 4t). The phase relation at the slot radiators varies in a continuous uniform fashion with the frequency. Thus the slot radiators 4u are fed in phase controlled relation. The radiation emitted from the individual slots 40 combines into a single beam of selectively variable direction dependent upon the frequency.

It should be noted that the interconnectingv sections 28 at the ends of each of the straight waveguide sections 22 may be either unitary, as shown, or comprised of separate members. The angular position or attitude of the slot apertures/46 with respect to each other may be varied in different manners in accordance with slot radiation theory and practice. For example, the slots at each end of the row of slots may be relatively parallel while the slots at the center may be at a marked angle to the row. Such variations, well understood by those skilled in the art, are merely pointed out here for the purpose of making clear that the characteristics of the beam provided may be varied in accordance with the installation and the purposes which it is sought to accomplish.

The scanning antenna or continuous waveguide arrangement 25) thus provided provides a very simple means for supplying a fan beam. At a center frequency, the beam thus provided is directed in what may be regarded as a zero. direction in a given plane. As the frequency applied is changed, the direction of the beam axis shifts about the zero direction in the given plane. The scanning antenna ZS shown in FIG. l would, by itself, generate a beam narrow along the launching line and fanshaped in a plane normal to the plane of the waveguides 22 and the energy launching line. With shifts in fre quency from a center value the fan-shaped beam would retain its narrow width but wouid incline or scan down on one side toward the plane of the waveguides 22.

The radiating apertures 40 in the continuous waveguide arrangement are placed along the launching line normal to the zeroy direction in the azimuthal plane. The combined beam provided from the radiating apertures 4i) mayA thus be said to be a launching beam, to distinguish the energy thus radiated from the energy which is directed into space, which is referred to below as space radiated or space propagated energy. The corrugated wave trapping surface member lo, therefore, is hereafter referred to as having a launching end portion, which is the portion adjacent the radiating apertures 4t), and a space propagation end portion at the extremity thereof which guide sections 25 is 'furthest from the radiating apertures 40. S/een in plan view, the space propagation end -may have a hemispherical shape which is substantially symmetrical with the given axis, which is the zero direction.

The corrugated surface wave guiding member may be physically mounted adjacent the continuous waveguide arrangement 20 by dielectric spacers 42 which mechanically support and which may electrically separate the corrugated surface member 10 from the continuous waveguide arrangement Zi). A Wave energy splash plate 44, consisting of an elongated wave energydirecting member having an angular or curved cross section, may be aixed along the launching line to divert the launching beam onto the launching Aend of the corrugated surface wave lmember lil. The splash plate 44 need not have a special configuration, as long as energy is diverted from a direction substantially normal to the continuous waveguide arrangement Ztl to a direction of substantial inclination toward theazimuthal plane. A dielectric or other closure member t6 which is substantially transparent to electromagnetic wave energy may be employed to close the opening defined by the free end of the splash plate member 44 and the surface of the corrugated wave guiding surface member i0. This Wave energy window 4d, which may be of polystyrene or other suitably transmissive material, may be mounted at an angle of inclination with respect to the azimuthal plane to provide a fairing or streamlining surface for the mounting of the complete antenna of this invention. A source of frequency shift energy 50 is coupled to the input section of the continuous waveguide arrangement 20. By the term source of frequency shift' energy it is intended to include energy sources which provide a continuous range of frequencies or successive steps of frequencies over the desired range. Either such source will result in a jbearn scanning `over a given angle from the continuous waveguide arrangement.

A brief description of the operation of the arrangement of FIG. 1 will first be provided. The source of frequency shift energy 50 may be operated over a given range of frequencies with a continuous variation between the limits of the frequencies employed. The energy thus fed to the continuous waveguide arrangement 20 therefore results in the provision of energy in phase controlled relation to the individual radiation apertures 40 in the continuous waveguide arrangement 20. The phase relation between these individual radiation patterns is such that a launching beam is formed which scans an angle on each side of a direction normal to the azimuthal plane. The splash plate 44, however, diverts this energy from a beam substantially normal to the corrugated wave trapping surface 10 to a beam having a planar front which is sharply inclined toward the corrugated wave trapping surface 10. in accordance with the operation of a corrugated surface when energy is launched thereon, the energy is confined from the launching beam into a surface wave transmitted along the length of the corrugated surface member 10 in a direction across the lands 12 and grooves 14. Details of the manner in which the energy isforrned into the surface wave are described in more detail below. The surface wave is subsequently launched from the space propagation end of the corrugated surface member 10 and is directed into space. The direction of launching of the energy in space is dependent upon the frequency applied to the continuous waveguide arrangement 29. Arrows have been employed to indicate some of the possible directions in whichf the beam may be launched relative to the corrugated surface 10. The 'disposition of the corrugated surface antenna lib and the continuous waveguide arrangement 20 operates to provide a controlled fan beam of desirable pattern whether or not the direction of the beam is normal with respect to the lands 12 and grooves 14.

An antenna so constructed is suitable for mounting in amobile installation, such as in an aircraft wing installation 6i), as shown in FIG. 2. The remainder of the airv the aircraft and 6 craft is not shown. With reference to FIGURE 2, it may be seen that the wave guiding structure 10 is substantially flush mounted with the leading portion 62 of the aircraft Wing 60 and that it canscan in the forward direction of at an angle to either side. .The same type of `an installation might of course be employed as scan up or down or from a point mounted flush with the cabin or vertical surface of the aircraft. The arrangement shown in FIGS. 1 and 2 has further advantages, in that the over-all silhouette is of small height. Consequently, the arrangement might be employed as part of a streamlined housing protruding from a main structure. It is of significance that no outer protective structure need be employed with this arrangement, so that aberrations in i Flo *s in three positions, where B=o, 8, and 15.

the beam do not result and extra physical assemblies are not needed. it would of course be possible and in some instances desirable to fill the grooves of the structure shown in FIG. l with a material such as ceramic or to cover the entire corrugated surface Siti with a material which is transparent to electromagnetic wave. energy.

The arrangement provided by this invention lmakes feasible the controi of beam shape as well as electronic control of the beam direction. ing an area in order to identify the position of other objects it is usually preferable that a fan beam having what is known as csc2 i9 elevation distribution'be employed. Such a beam is considered as a fan beam and is usually relatively narrow in azimuth. Disregarding the side lobes usually present, which are relatively minor, such a beam appears in elevation as is shown in FIG. 4. The cosecant-squared beam has a fairly regular lobe on the positive side of its zero elevation' axis which is in the azimuthal plane)V and has a sharp cutoi on the lobel on the negative side of the azimuthal plane. For purposes of operating a system for detecting and monitoring the position of objects, it is extremely important that the regularity of this beam be maintained over an entire scanning angle, as far as possible. The present invention permits provision of this desirable beam shape, as is shown in the charts of PEG. 3. These charts illustrate the signal strength of the beam in elevation from the azimuthal plane, which is taken as H0, for successive angles of deviation from the zero direction. The scanning angle from the zero direction, here called B is shown in In each case it may be observed that there is excellent power in the direction of the beam, the desired rise in power on the positive side of the beam and the d esired sharp drop Y in the lobe on the negative side of the beam. The details of arrangement of the surface and the corrugations by which this is achieved, together with the other elements of the combination, are described in greater detail below. It should be recognized that the angle 00 with respect to g the plane of the corrugated surface 10 may be zero or may be varied within limits is still spoken of herein, plane.

The art of employing a corrugated surface to control the radiation from a beam in one direction only has been known and investigated for a considerable period.' Reference may be made, for example, to the teachings of Cutler in Patent No. 2,659,817 issued November 17,

on either side. The scanning however, as 'being in the azirnuthal 1953. As shown in this reference, various surfaces, such as square corrugations, triangular or round corrugations and spaced septa may be employed to guide the electromagnetic waves transmitted across the surface. Waves which are guided in this manner have a surface velocity which is less than the velocity of the waves infree space. The waves have a longitudinal component of electric field which is transverse to the corrugations across which they travel. The spacing between the corrugations and the depth of the corrugations determine the propagation velocity for a wave which is normal to the corrugations. It is also possible, however, by the use of this invention to employ these relationships so as to determine with For purposes of searchregularity over a substantial angle the surface velocity of energy transmitted at an oblique angle to the corrugations. Further, however, the arrangement thus provided makes possible variations in the corrugated surface which permit adjustment of the gain provided by the antenna and control of the shape of the beam which is propagated into space. Consequently the energy radiated as a launching beam is converted into a space propagation pattern of selected configuration and having controlled characteristics over the scanning angle.

As to the control of the surface wave velocity with respect to the free space velocity, it is known that the trapping can be increased and the speed slowed by increasing the groove depth and by increasing the number of corrugations per wavelength.

In one practical embodiment of this invention, the corrugated surface member was constructed with a geometry of d/}\=0.0953 and h/}\=0.0648, with d/ and h/ being the gap width and the tooth depth respectively. Such a configuration may be used over the principal corrugated surface, although various modifications may be made at the energy launching end and at the convexedged space propagation end.

Some of these modifications are illustrated by cornparison of the structure of FIG. l. The teeth of the surface wave structure of FIG. may be, as shown, thin plates or vanes 13 instead of the square corrugations of FIG. 1. These vanes 1.3 may vary in height along the direction of travel of the surface wave, and the substantially planar surface itl may be modified by arcuate portionsl at either or both ends along the direction of wave trapping. For example, as shown in FG. 5, the end at which energy is launched onto the corrugated surface member may be curved upwardly as viewed in FIG. 5) from its launching edge to receive the energy provided in the launching beam. Similarly, at the space propagation end of the corrugated surface member 10, there may be a downward curve which, alone or together with the depth and spacings of the vanes 1.3, makes possible the :attainment of the desired beam shape and position (in the elevation direction) of the maximum of the beam. With the approximate configuration shown the cosecantsquared beam pattern may be achieved, or patterns of other desirable characteristics may be attained if desired.

It is extremely important to note that with the types of configurations shown in FIGS. l and 5 there is no significant degeneration of the beam shape when the beam is launched across the corrugated surface in a direction which is skewed or oblique to the direction of the corrugations. It would appear upon first examination that a beam launched at an angle across corrugations would not be properly controlled as a surface wave, because it is known that when a component of electric field vector is parallel to corrugations there is no surface wave effect. because no trapping can take place. Such degeneration of the beam with a skewing relative to the corrugations does not take place. The beam retains a substantially cosecant-squared pattern despite displacement from the selected direction. It is assumed that control of the surface wave is maintained because of the manner in which the energy is launched and maintained in a planar front. because the wave trapping is not operated in a critical mode, and because the component of the electric vector which is normal to the corrugations exerts a great influence on trapping, and thus on the velocity of the surface wave. There is, for this hybrid surface wave, no electric vector component which is parallel to the corrugations. Therefore the surface wave velocity changes only slightly despite displacement of the combined beam from the zero direction.

Antennas such as are provided in FIGS. 1 and 5 can be modified in other ways than by curving or tapering the corrugated surface member to control the beam pattern. A wave trapping surface can in addition be adusted to selected conditions, to achieve desirable amounts of gain, as by varying the ratio of the surface wave velocity to the free space velocity for the length of antenna involved. Those skilled in the art have available various analytical techniques by which maximum gain may be achieved given the operating wavelength the length of the corrugated surface and the other conditions involved.

In practice greater gains are obtainable with longer surfaces. A typical antenna has a length of the corrugated surface member 1l) over which the surface wave travels of approximately ten operating wavelengths for the median frequency employed. For this type of structure, it is usually alsopreferable that the launching portion, such as the curved launching segment shown in FIG. 5, should be of the order of two operating wavelengths.

A different arrangement, by which an entire structure may be substantially ush mounted, is shown in the arrangement of FIG. 6, to which reference is now made. in this arrangement, a plurality of continuous waveguide arrangements 7G, 71, '72 are employed. Each of the first, second and third continuous waveguide arrangements 70, 71, 72 is related to the continuous waveguide arrangement 20 of FIG. l and provides a continuous sinuous path in like manner. In the arrangement of FIG. 6, however, the radiating apertures 74 are positioned in the broad wall portions of the interconnecting terminal sections. The radiating apertures 74 lie in a plane defined by the ends of the continuous waveguide arrangements 70, 71, 72. The radiating points which are thus defined lie in the azimuthal plane of the corruga ed surface member 10. The corrugated surface member 10 may include a cover plate 11 which extends across the ends of the continuous waveguide arrangements 70, 71, 72. The cover plate 11 is apertured to correspond to the radiatingr apertures 74 and provides a flush surface.

Each of the continuous waveguide arrangements 70, 71, 72 of FIG. 6 lies in a plane substantially normal to the azimuthal plane, the planes of these continuous waveguide arrangements 70, 71, 72 being parallel and adjacent and the arrangements 76, 71, 72 providing coextensive and adjacent waveguide groupings. The apertures 74 positioned in the curved connecting sections of the continuous waveguide arrangements 7%, 71, 72 are in this instance mounted substantially parallel to the plane of the waveguide arrangements 70, 71, 72, so as to be responsive to the electric vector of the energy transmitted along the continuous waveguide arrangements 70, 71 or 72. in accordance with known radiation pattern forming techniques, the radiation apertures 74 in each line may be placed along a central axis or spaced slightly to either side of the central axis of each waveguide arrangement 70, 71 or 72.

A single frequency shift source of energy 5|) may be employed with the plurality of continuous waveguide arrangements 70, 71, 72. A first of the continuous waveguide arrangements 70 may be coupled directly to the frequency shift source `of energy. The succeeding second and third continuous waveguide arrangements 71 and 72 may, however, be coupled to the frequency shift source of energy 50 through individual first and second phase shifter devices 76 and 78 which provide successively increasing amounts of phase `shift to the energy from the frequency shift source of energy 50.

With the amount of phase shift provided from each of the phase shifters 76 and 78 being properly selected with respect to each other, in accordance with well known techniques, the radiation patterns provided from the continuous waveguide arrangements 70, 71, 72 unite into a single beam which is inclined with respect to the azimuthal plane. The operation of the :arrangement of FIG. 6 may thus be understood as involving an azimuthal scanning following inclination of the beam into the launching portion of the wave trapping surface 10. The azimuthal scanning in the :arrangement of FIG. 6 is Y scanning antenna having excellent achieved in a manner similar to the arrangement of FIG. 1. "Ihat is, as the frequency of the applied energy is changed, the phase Yrelation of the radiation from the apertures 74 in each continuouswaveguide arrangement 70, 71 or 72 is likewise changed to provide a combined fan beam which would scan in the plane of the waveguide arrangements ,70, 71, '72 normal to the azimuthal plane. The presence of the iirst and second phase Shifters '76 and 78 between second and third continuous waveguide arrangements 71 and 72, however, alters the direction of the single resulting beam so that the single resulting beam is inclined in the direction of the corrugated surface member and is trapped thereby. The angle of inclination of the single resulting beam can be modified with respect to the azimuthal plane, within limits, but will be sufficient to cause the wave trapping to occur. If needed, Vgreater tooth depth and gap spacing can be employed to assure greater wave trapping.

Once the surface wave has been created in the corrugated surface member 10, the resultant beam scanning pattern, varying about a zero direction in the azimuthal plane, is achieved in the manner described in conjunction with the description of the operation of FIG. 1.

The arrangement of FIG. 6 will be appreciated as having particular adaptability to flush mounted installations. The entire corrugated surface 10 and the radiatingapertures 74 may be lled, if desired, with a low loss dielectric material, such as a Aceramic (not shown). Whether or not such a technique is employed, however, a

beam pattern characteristics is provided which is structurally extremely strong and simple to fabricate. Furthermore the rigidity of the device and its independence of operating characteristics insures reliable satisfactory operation under adverse conditions of placement and use.

An arrangement which is particularly suited for frequencies of operation somewhat lower than the applications which the above described arrangements might be employed, such as in the ultra high frequency range, is shown in FIG. 7. Referring to FIG. 7, the arrangement there provided includes a plurality `of radiating elements, such as dipole radiators 80, mounted along an energy launching line. The dipole radiators 80 are mounted against a first ground plane member 82 which may be comprised of a metallic plate but which preferably, as shown in FIG. 7, consists of a grid of conductive Wires. Such a grid 82 may be effectively employed for a ground plane provided that the spacing between parallel wires is less than one fourth of the operating Wave lengths employed. In this arrangement, each of the dipole radiators Sti may be fed, as by a coaxial line (shown only schematically), with energy of a dierent phase. The desired phase control relation is achieved in the illustrative example of FIG. 7 by coupling energy from a source of energy of fixed frequency 84 to each of the dipole radiators 8@ through a different variable phase shifting device 86. The phase relation of energy provided to the dipole radiators 4Si) may be changed, and the beam provided caused to scan, `by employing a ganged cyclically operating arrangement for driving the variable phase Shifters 86. In the present arrangement the variable phase Shifters v36 are, as shown in simplified form, coupled together and driven together from a mechanical actuating means 83. The rotation of a drive shaft, for example, by the actuating means 88 may be used to provide the ganged cyclical operation. Although a number of variable phase Shifters are available in the art, and although a number of mechanical or electrical means will suggest themselves for providing phase shifts in a selected pattern, a particularly suitable arrangement is provided in an application entitled Mechanical Phase Shifter, Serial No. 529,557, now Patent No. 2,836,821, led August 19, 1955, by R. S. Elliott and K. C. Kelly, and assigned to the assignee of the present invention. The invention there described employs a corrugated rotatable drum having a shaped peripheral configuration, in conjunction with a parallel plate transmission line arrangement and a parallel of probes. As the shaped surface of the corrugated drum is rotated adjacent the transmission line plate and the probes, energy of a variable selected phase relation is provided to each of the probes. A fuller understanding of the operation of such a phase shifter may be appreciated by reference to the above copending application.

The wave trapping surface 10 in the arrangement of FIG. 7 is provided by a plurality of coplanar substantially parallel linear conductive elements or rods 96, separated by dielectric or other insulative spacers 92 from a Second ground plane surface 94 made up of a plurality of wires or other conductors arranged like the first ground plane member 82. 'Ihe term corrugated surface member as used here is intended to include such an arrangement of linear elements 90 separated from a conductive ground plane 94. The `pacing between the linear rods 90' or wires in the azimuthal plane in which they are principally located, and the separation of the linear rods 90 from the ground plane, determine the extent of the wave trapping and the surface velocity of the waves, as in the arrangement of FIG. l. The rods 90 may also be separated from the second ground plane 94 by conducting wires (not shown); this construction would be a corrugated surface Y made of rods and wires.

The arrangement of FIG. 7, which is particularly suit` able for operation in the ultra high frequency range and in relatively fixed installation, operates as follows. Energy of a single frequency provided from the source of fixed frequency energy 84 to the phase Shifters S6, is provided thereby to the individual dipole radiators 80. Simultaneously, the ganged phase shifter devices 86 are varied in a predetermined manner by the actuatingmeans 88 to cause energy to be fed in the desired phase relations to the dipole radiators Si). Co 1sequently, there is provided a launching beam which varies about a zero direction in the azimuthal plane and swings to a maximum on each side of the zero direction, as the variable phaseshift devices S6 are changed through a cycle of operation. 'I'he principal axis of the launching beam from the dipole radiators 89 has here been selected to lie in the azimuthal plane. Consequently, the launching beam is trapped by the wave trapping surface 10, transmitted along the WaveV trapping surface 10 as a surface wave and propagated into space from the space propagation end which is spaced apart from the dipole radiators 80. As with the arrangements of FIGS. 1, 5 and 6, the control is maintained over the beam through an angle as great as 45. Thus the beam has substantially like characteristics through such an angle despite its Obliquity to the wave trapping surface 10.

As with the antennnas of FIGS. 1 and 5 the elevation pattern may be controlled and enhanced by varying the rod of wire diameter, spacing and height above ground plane, especially at the two ends.

Thus there has been provided a scanning antenna arrangement which generates a contorlled beam through a scanning angle in a given plane. The arrangement may be utilized to control the radiation pattern provided, to provide superior physical configurations and to achieve reliable and stable operation.

I claim:

1. An antenna comprising: a plurality of radiators disposed along a launching line and fed in phase controlled relation whereby a well defined beam will be radiated in a predetermined direction, means for varying said phase relation for Varying said direction of said beam throughout a given scanning angle, and means including a wave trapping surface having conductive discontinuities disposed substantially parallel to the launching line and arranged to trap electromagnetic wave energy in said beam from said radiators, said Wave trapping surface lying principally in a given plane and radiating into space spaanse l i a controlled pattern of energy throughout said scanning angle lying substantially within said plane.

2. A scanning antenna for radiating a beam within a scanning angle which lies substantially symetrically about a given axis and in an azimuthal plane and comprising: a plurality of radiating elements lying adjacent said azimuthal plane along a second axis substantially normal to Said Agiven axis, said radiating elements being disposed substantially symmetrically with respect to said given axis; means coupled to each of said radiating elements for providing energy thereto whereby said elements will radiate a well defined beam of electromagnetic energy, and a plurality of spaced conductive elements lying principally along said azimuthal plane and substantially parallel to said second axis so as to form a surface wave trapping structure, said surface wave trapping structure being substantially symmetrical with said given axis and positioned to convert the radiation pattern from said radiating elements into a space propagation pattern of selected configuration, control means effective to cause said beam to sweep across said structure to thereby vary the direction of said propagation pattern in said azimuthal plane.

3. A scanning antenna comprising: means including a plurality of radiating elements spaced along a given axis for providing an energy launching array; i eans coupled to said radiating elements for providing energy of selected phase relation to the individual radiating elements of a predetermined phase relation whereby a beam of energy will be radiated from said elements, means for varying said phase relation whereby said beam will scan through a given angle, and a wave trapping device of the surface irregularity type having spaced members lying in lines parallel to said given axis, said spaced members lying principally along an azimuthal plane and having selected relationships to convert the launching beam into a space radiation pattern having controlled characteristics for eachposition of said beam within said scanning angle lying within said azimuthal plane.

4'. An electronic scanning antenna having a small dimension in an elevation direction above an azimuthal plane, said antenna scanning about a selected direction in said azimuthal plane with a substantially cosecantsquared elevation beam, said antenna comprising: a plurality of radiating elements disposed in a plane parallel to said azimuthal plane and substantially normal to said selected direction; energy feeding means coupled to said radiating elements and feeding said radiating elements individually with energy of selected phase relation, such that the combined radiation pattern from said radiating elements is a launching beam which varies in direction about said selected direction as said phase relation is changed; and a wave trapping member having a ground plane portion and conductive surface discontinuities disposed in parallel lines normal to said selected direction and lying principally in said azimuthal plane, said wave trapping member including a launching end adjacent to said radiating elements for trapping beam energy radiated therefrom, said discontinuities being varied with respect to each other and said ground plane portion along the selected direction from the launching end to confine energy emitted from said radiaing elements into a substantially cosecant-squared beam despite displacement of the beam from the selected direction in the azimuthal plane.

5. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities that are arranged to form an input section and a launching section, radiating element means disposed adjacent said waveguiding surface for radiating a well defined beam of electromagnetic energy onto said input section so that said beam will be guided across said surface, means operatively interconnected with said radiating means for varying the direction of said beam throughout a given scanning angle whereby said beam will sweep across said surface, said launching section including at least one disl continuity in said irregularities whereby the energy in said beam will be radiated into space in a predetermined pattern having a direction determined by the direction of said beam.

6. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities, at least one waveguide path having a plurality of radiating apertures therein disposed in a line substantially parallel to said irregularities for radiating a Well defined beam of electromagnetic energy onto and across said guiding surface, means for controlling the phase of the excitation of said apertures for controlling the direction of said beam throughout a scanning angle, said waveguiding surface lying principally in a given plane and including a launching portion for radiating into space a controlled pattern of the energy in said beam, the direction of said pattern being controlled by the direction of said earn within said scanning angle.

7. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities disposed generally in a plane so as to form an input section and a launching section, at least one sinuous waveguide path having a plurality of radiating apertures therein disposed in a line substantially parallel to said irregularities for radiating a beam of electromagnetic energy, means for directiing said beam onto said input section of said surfaceV whereby said beam of energy will be guided across said surface, means for controlling the phase excitation of said apertures for controlling the direction of said beam throughout a scanning angle whereby said beam will sweep across said surface within said angle, said launching section including discontinuities in said irregularities whereby said energy will be radiated into space in a controlled pattern having a direction determined by the direction of said beam.

8. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities that are arranged substantially in a plane to guide electromagnetic energy thereacross, a plurality of groups of waveguides having radiating apertures disposed substantially in said plane for radiating electromagnetic energy therefrom, the apertures in a given group being disposed in a line substantially normal to said irregularities and excited to direct the energy therefrom into said plane, the relative phases of the radiated energies from said groups forming a resultant beam of electromagnetic energy that is propagated into said plane and along said surface, said waveguiding surface lying principally in said plane and radiating into space a controlled pattern having a direction determined by the direction of said beam.

9. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities disposed to form a substantially plane input section and a launching section, a plurality of groups of waveguides having radiating apertures disposed substantially in said plane for radiating electromagnetic energy therefrom, the apertures in a given group being disposed in a line substantially normal to said irregularities and excited to direct energy therefrom onto said input section whereby said energy will be guided by said irregularities, the radiated energies from said groups having related phases for forming a resultant beam of electromagnetic energy that is guided along said input section to said launching section, said launching section including at least one discontinuity in said irregularities whereby said energy will be radiated into space in a controlled pattern having a direction determined by the direction of said beam.

10. An antenna comprising a waveguiding surface having a plurality of substantially parallel conductive irregularities arranged substantially in a plane to guide electromagnetic energy thereacross, a plurality of dipole radiators arranged to form an array disposed along a launching line substantially parallel to said irregularities, means for feeding said dipole radiators in phase controlled relation whereby a well defined beam will be radiated onto 13 said guiding surface in a predetermined direction, means for varying said phase relation for varying said direction of said beam throughout a given scanning angle whereby saidY lbeam will sweep across said guiding surface, said waveguiding surface lying principally in said plane and including a launching portion effective to propagate into space a controlled pattern of energy having a direction determined by the direction of said beam.

1L An antenna comprising a waveguiding surface having a plurality Yof substantially parallel conductive irregularities arranged torform a substantially plane input section and a launching section which are effective to guide electromagnetic energy thereacross, a plurality of dipole radiators arranged to form an array adjacent said input section and arranged along a launching line substantially parallel to said irregularities, means for feeding said dipole radiators in phase controlled relation whereby a well defined beam will be radiated onto said input section in a predetermined direction, means for varying said phase relation for varying said direction of said beam throughout a given scanning angle whereby said beam will sweep across said guiding surface, said launching portion including at least one discontinuity in said irregularities and being effective to propagate into space a controlled pattern of energy having a direction determined by the direction of said beam.

References Cited in the lile of this patent UNITED STATES PATENTS 2,411,032r Gluyas et a1. Nov; 12, 1946 2,418,124 Kandoian Apr. l, 1947 2,624,003 Iams Dec. 30, 1952 2,659,817 Cutler Nov. 17, 1953 2,676,257 Hebenstreit Apr. 20, 1954 FOREIGN PATENTS 983,033 France f Feb. 7, 1951 

